The present invention relates generally to systems and methods for minimizing or preventing deep vein thrombosis (DVT) and maintaining the body temperature of a person under anesthesia, and specifically to systems and methods that incorporate applying heat and compression in furtherance thereof.
Deep vein thrombosis (DVT) relates to the forming of blood clots (thrombi) in the deep veins of the body, usually in the pelvis, thigh, or calf. This can result in severe complications—including death. One of the causes of DVT is surgery. The body of an anesthetized person undergoing surgery loses the ability to regulate temperature because the body is paralyzed. The operating room is preferably maintained at lower temperatures. Thus, body temperature drops as a result. This drop in temperature increases the risk of DVT and increases post-operative recovery time (i.e. length of time outpatient must wait before being released). The body temperature of an anesthetized person can fall as low as 92 deg F. It is preferable to maintain the body at around 98.6 during surgery.
Various solutions (aka DVT therapy systems) have been proposed to maintain the body temperature during surgery. For example, an air filled blanket has been used wherein heated air is delivered. One such systems is the “BAIR HUGGER™ Warming Blanket”, sold by Cardinal Health. Such solutions are problematic because the blanket and interconnecting hoses are relatively large and cumbersome and tend to interfere with the surgeon needing access to various parts of the body. Additionally, the large, inefficient apparatus used to heat and deliver pressurized air wastes heat that results in a detrimental increase in room temperature.
Another solution involves applying intermittent (pulsed) compression to the calf by wrapping a fluid filled bladder (contained within a fabric sleeve—aka calf garment) around the calf. One such system is the VASOPRESS™ sold by Compression Therapy Concepts utilizing a calf garment model “VP 501M”, and compressor model number “VP 500”. The foregoing is also collectively referred to herein as a “compression system” or “DVT therapy system”, etc.
Some systems have been modified to apply heat to the fluid. However, such systems are inefficient because the heat must be transferred to the fluid, then delivered to the bladder, then transferred from the bladder to the calf.
The present invention overcomes the foregoing problems as well as achieves other objects and advantages that will be apparent to those of skill in the art by utilizing a heating element (flexible heating pad, or air-activated heat pack) in conjunction with a compression bladder.
In one embodiment, an electrically energized flexible heating pad is used. The flexible pad is electrically heated and thus it delivers heat more efficiently than fluid based systems because the conventional intermediate heat transfer medium (fluid) is eliminated. The heating pad is restrained against the inside of the bladder/sleeve combination by a removable, disposable sheet situated between the skin and the bladder. The heating pad can therefore be reused because it does not come in contact with the skin. The sheet and bladder are discarded.
Flexible heating pads are known. One such device is the “Flexible Silicone Rubber Fiberglass Insulated Heater” sold by OMEGA ENGINEERING, INC™. They come in rectangular or round shapes in varying wattage per square inch and are available in either alternating or direct current configurations. Additionally, they can be driven by either varying or pulsed voltages. The flexible heating pad is advantageous because it can wrap around the calf and move along with the intermittent compressions of the compression system.
It is essential that a safe surface temperature be maintained to prevent injury to the anesthetized patient who is unable to communicate. The surface temperature of the flexible heating pads can exceed 400 deg F. It is preferred to establish a temperature threshold at 105 deg F. to prevent injury. The electrical energy used to heat the pad is regulated to achieve this. The temperature of the heating pad is regulated by a feedback loop which incorporates a temperature probe placed against the patient's leg. Alternatively, a temperature probe and shutoff circuit is employed.
Although not essential, it is advantageous to use a low, direct current voltage to energize the heating pad. This is advantageous because conventional 60 hertz AC power can interfere with the body's nervous and cardio vascular systems. It is also advantageous (but not essential) to provide electrical energy from a battery. This is advantageous because the battery/heating pad system is electrically isolated thus reducing the chance of shocking the patient.
The air-activated heat pack fits inside of the air bladder and is activated and heated as pressurized air is intermittently applied. Air-activated heat packs are known in the art. A popular variety utilizes iron, water, cellulose, vermiculite, activated carbon, and salt. An example of such a heat pack is the GRABBER™ brand (www.warmers.com). These heat packs are nicely applied to conventional DVT therapy systems that utilize pressurized air (e.g. intermittent (pulsed) compression systems). The air delivery of these systems serves an additional purpose. Exposure to the pressurized air causes the heat pack to heat up without the need for externally (e.g. electrical pad, heated fluid) generated heat. This offers several advantages including eliminating the risk of electrical shock and connection wires, and also cost effectiveness.
The present invention incorporates air-activated heat packs with conventional pressurized air DVT therapy systems to provide a cost effective, efficient means of adding heat to pressurized therapy. The heat packs are contained within the air bladder (aka internal chamber) of the calf garment. The combination must be stored, until just prior to use, in an air-tight package to prevent premature activation.